System for refrigerated lpg storage



March 28, 1961 P. MEADE SYSTEM FOR REFRIGERATED LPG STORAGE Filed April 22, 1959 FIG.

L35 viii INVENTOR.

L. P. MEADE M (W ATTORNEYS FIG. 4

United States Patent SYSTEM FOR REFRIGERATED LPG STORAGE Leonard P. Meade, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 22, 1959, Ser. No. 808,156

11 Claims. (Cl. 62-54) This invention relates to storage of liquefied gases. In one aspect it relates to the storage of such liquefied gases as liquefied propane, liquefied butane, mixtures thereof, an anhydrous ammonia.

As a specific example of this invention I will describe a method and apparatus for the storage of liquefied propane at pressures very near atmospheric pressure.

By the term propane as used herein is meant pure propane, or commercial propane, the latter usually containing a small percentage of ethane and some butane. The physical properties of commercial propane will obviously diifer from the physical properties of pure propane, as understood by those skilled in the art.

Because of their high vapor pressures at atmospheric temperature, liquefied gases, such as liquefied propane, require high pressure storage vessels, or low pressure storage vessels thermally insulated and their contents maintained cool by artificial cooling. Large capacity refrigeration units are frequently used in an atempt to maintain low pressure storage through low temperature. The amount of refrigeration required even in large LPG (liquefied petroleum gas) storage installations, as required by utilities, is not especially large when the storage facilities are properly insulated.

When refrigeration requirements are reduced through proper insulation of tanks and pipes, maximum refrigeration loads occur at times when tank cars, transport trucks or pipeline quantities of liquefied gas are transferred to the storage tanks. It is obvious that a large quantity of warm liquefied gas may warm a small volume of liquid in a storage tank to such a temperature that the resulting vapor pressure in the tank may be too high for safe storage. In this case, the liquid to be stored should be cooled prior to transfer to storage. A refrigeration unit sufficiently large to cool one or more tank cars of liquefied propane from, say, 100 F. to a desired storage temperature of well below 0 F. at normal unloading rates would be greatly oversize for temperature maintenance during storage. Since refrigeration units are expensive equipment, it is desired to use as small a unit as possible. Another point which allows a considerable saving in first cost is to store theliquefied gas at as low a pressure as possible so as to eliminate need for the use of pressure storage vessels. When storing liquefied propane, which has a vapor pressure of approximately 184 p.s.i.g. (pounds per square inch gauge), at atmospheric temperature thick walled vessels are required. Thus, by storing propane at a temperature near its normal boiling point, I am able to employ relatively thin walled vessels. When storing liquefied propane in quantities of a million gallons or more, storage at low pressures greatly reduces capital investment in tankage costs. By the application of this invention, I am able to use a relatively small refrigeration unit to serve the two-fold purpose of temperature maintenance during storage and cooling of the liquefied gas during transfer of incoming liquefied gas to the storage vessel orvessels.

For practicing this invention, I use a refrigeration or R 2,976,695 Patented Mar. 28, 1961 cooling unit of a size only slightly larger than that required for mere temperature maintenance of full storage. The excess refrigeration or cooling over that required for temperature maintenance is stored up in a refrigeration vessel for use during LPG unloading periods. In this manner I am able to use a refrigeration or cooling apparatus at full capacity, which operation allows efficient operation.

An object of this invention is to provide a method for' low pressure storage of liquefied gases. Another object of this invention is to provide a method for the low pressure storage and for unloading liquefied gases such as propane, butane, and anhydrous ammonia, from atmos Another object of this invention is to provide apparatus and a method for' the operation of such an unloading and storage system. Yet another' pheric temperatures.

object of this invention is to provide a' refrigeration storage unit which is suitable to operate in conjunction" with a refrigeration apparatus forcooling liquefied petroleum gas during unloading times at rapid rates and: for storage of refrigeration during storage periodsli Other objects and advantages of this invention will be.

apparent upon reading the following description and drawing which respectively describes and illustrates preferred embodiments of my invention.

In the drawing Figure 1 illustrates in diagrammatic form a preferred form of apparatus for practicing my invention. Figures 2, 3 and 4 illustrate diagrammatically alternate embodiments of a portion of the appathick layer of insulation 12 is provided as a cover for the entire tank. A pipe 15 communicates the upper portion of tank 11 with a cooling coil- 17 which is operated as a condenser. Pipe 15 is provided with a com pressor 16 for compression of vapor from tank 11 with;

A pipe 38- its ultimate passage to the condenser 17. leads from the condensate outlet end ofcondenser 17 to a surge tank 19 which is illustrated as containing a liquefied gas 21. V A vessel 13, herein called a refrigeration vessel, is also" provided with a thick layer of insulation 14. Disposed in vessel 13 is a heat exchange coil 28. Pipe 25 connects the surge tank 19 with a pipe 26 as illustrated. Pipe 26 communicates with the inlet end of the heat;

exchange coil 28. An insulated pipe leads from the other and outlet end of coil 28 to the storage tank 11. A

pipe 31 is for inlet or outlet of refrigeration storage medium. Disposed within the storage tank are sprays 37. Sprays 37, if desired, are disposed as spray nozzles mounted in the bottom of spray ring 39. The pipe 36 I leading from coil 28 is attached to the inlet end of the spray ring 39. Surge tank 19 is provided with a liquid level sensing means 23, such as a float, and pipe 25 is provided with a valve 24, as illustrated. Reference numeral 22 identifies a controller which actuates valve i 24 in response to a liquid level as sensed by sensing means 23.

A tank car 33 is illustrated as a source of liquefied gas for transfer to the storage system. A- pipe 27, conraining a check valve 40a and one or more valves 40,

communicates the tank car 33 with pipe 26 at its point of communication with pipe 25. The surge tank 19 is provided with a relief valve 20 in case pressure relief I.

ever becomes necessary. A motor driven fan assembly 18 is provided for passing cooling air over the condenser 17. A vent 29 is provided for'atmospheric breathing in refrigeration tank 13. Pipe 32 is for outlet of stored liquid.

Refrigeration tank 13 is provided with a quantity of a refrigeration medium 34, such as water, sodium chloride, or calcium chloride brine or other liquid suitable for storing large quantities of refrigeration, such as aqueous ethylene glycol. In case butane is stored at a pressure near atmospheric pressure, water can be used as a refrigeration storing medium. According to this invention, 'it is intended that the refrigeration storing medium 35 be frozen as a solid. If a liquid having a high specific heat and a freezing point below the normal boiling point of propane were available, such a liquid could be used according to my invention. However most liquids such as low freezing hydrocarbons do not have particularly high specific heats and such materials, while operable according to my invention, are not preferred. I prefer to use either water or an aqueous brine or other aqueous solution because, as is known, water has a relatively high specific heat. Furthermore, when an aqueous brine solntion or other aqueous solution freezes at refrigeration temperatures, a large amount of refrigeration is available because water also has a very high heat of fusion.

When using an aqueous brine or other aqueous solution as a refrigeration storing medium 34, part or all of it may become frozen during the storing up of the refrigeration. When water solutions such as salt and water, or calcium chloride and water, or ethylene glycol and water are frozen, the frozen mass will be slushy at first and will not harden until after its temperature has been decreased to. a temperature considerably below the temperature of the formation of the first crystals of ice. In this manner, large quantities of refrigeration can be stored before the storage medium becomes fully solidified; however, a fully frozen and solidified refrigeration storing medium is contemplated according to this invention, as well as the medium prior to its complete solidification.

When a system, such as the system hereindisclosed, is constructed and is ready for use, all parts obviously are at atmospheric or substantially at atmospheric tempera ture. Such a temperature is very high in comparison to the propane storage temperature as hereindisclosed. The system must be cooled down to the required Subzero temperature before it is in condition for storage of propane. The obvious refrigerant to employ for this initial temperature reduction step is propane itself. Thus, one or more carloads of propane are passed through pipe 27 and expansion valve 40. Upon passing through valve 40 the liquid propane is largely vaporized thereby cooling, at first, pipe 26. As soon as pipe 26 is cooled liquid passes into coil 28 in heat exchange with the refrigeration storage medium 34. In coil 28 violent boiling and complete vaporization occurs for a considerable length of time and until medium 34 becomes quite cool. Vapor and finally vapor and liquid pass from coil 28 through pipe 36 to sprayring 39 and through spray nozzles 37 into tank 11.

When sufficient vaporous propane accumulates in tank 11 to increase the pressure therein to l p.s.i.g., a pressure controller 16a starts a compressor which removes vapor and air from the tank. Motor valve 24 in pipe 25 is closed because liquid is not present in surge tank 19. For a considerable length of time on startup little to no propane condensate will be produced in condenser 17. Pressure in surge tank 19 will increase to a value at which relief valve 20 is set. This valve may be set at a pressure of, for example, 265 p.s.i.g. (pounds per square inch gage). Compressed gas, at first, will be largely air displaced from tank 11. Such compressed air will vent through the relief valve 20 until it is displaced from the system. c As the gas being withdrawn from tank 11 becomes richer in propane a time will be reached at which the propane concentration is sufliciently high in the compressed gas to be condensed upon passage through the condenser 17. Condensate passes into the surge tank 19. When the level of liquid propane in tank 19 reaches a predetermined level, as indicated by a liquid level sensing device 23, this device pulses controller 22 and then enna 4 controller causes expansion valve 24 to open. Upon opening of valve 24 the liquid propane from tank 19 expands through the valve to cool pipe 25 downstream of valve 24, and to cool pipe 26 and the refrigeration storage medium 34.

Thus propane vapor is withdrawn from tank 11, compressed in 16, condensed in 17, and condensate run into surge tank 19, from which the propane passes through expansion valve 24 to chill medium 34 and to chill storage tank 11. This propane recycling is continued until the storage tank 11 and the refrigeration storage medium 34 are cooled to the desired propane storage temperature. The refrigeration storage medium 34 will then usually be frozen solid. When all this equipment is thus properly chilled, the system is then in condition to receive propane for storage.

Under summer time conditions wherein the condenser is an atmospheric air condenser, temperature of the condensate is about F. or somewhat less than this value. At this temperature the accumulator pressure is about 265 p.s.i.g. Under wintertime conditions, the condensate temperature is somewhat below 120 F. for example, 90 F. At this lower temperature the accumulator pressure is well below the aforementioned 265 p.s.i.g., for example, about p.s.i.g. in the absence of noncondensible gas. When noncondensible gas is present, it accumulates in the surge tank 19 until pressure therein reaches the pressure at which the relief valve is set, which for exemplary purposes, is taken as 265 p.s.i.g.

There is no need to be advised of the specific pressure down-stream of valve 40 and valve 24. Pressure reduction in these valves will decrease from, for example, the aforementioned 265 p.s.i.g. to a value somewhat below 265' when there is violent boiling and complete vaporization of a large flow stream of propane in the refrigeration coil 28 because of the back pressure of the rapidly formed vapor. When the refrigeration storage medium has become well chilled, the rate of vaporization downstream of these valves is greatly reduced with the result that there is less back pressure on these valves. When the medium is fully chilled, the back pressure on these valves is only slightly greater than the l p.s.i.g. maintained in tank 11 plus the head of fluid between the level of the expansion valves and the level of the spray ring 39 plus that due to friction. Nozzles 37 do not restrict liquid flow therefore there is substantially no pressure drop through them.

When the refrigeration storing medium 34 is fully refrigerated, it is then in condition for passage of liquefied gas from a tank car, a truck, or a pipeline to storage. Liquefied propane as from a tank car 33 is passed through pipes 27 and 26 with valve or valves 40 therein being open. The compressor-condenser system is, of course, in operation and the liquefied propane from the tank car 33 passes through check valve 40a and valve 40 which allows a pressure reduction from tank car pressure to the pressure maintained in pipe 26. This pressure reduction chills the liquefied propane coming from the tank car and this liquefied propane is mixed with the propane passing through the pressure reduction valve 24. This combined propane then passes through the refrigeration coil 28 for further chilling by the refrigerant 34 prior to passage 7 to storage. Upon being sprayed through spray nozzles 37, the newly added propane, as well as the recycle propane, has a temperature substantially that of the desired propane storage temperature. It is intended that the amount of refrigeration storing medium 34 provided in refrigeration vessel 13 be sufficiently large that any required amount of new propane being passed to storage can be properly cooled prior to passage into tank 11. When one or more tank cars. of propane are so transferred to storage, an appreciable amount of solidified refrigeration storing medium may be melted without appreciable increase in temperature of the melted refrigerant. The heat of fusion of the refrigerant, is relied on to provide the refrigeration. After all the liquid propane is transferred from the tank car 33 through valve 40, valve 40 is closed along with any other valves in pipe 27, and the refrigeration cycle is continued for chilling and refreezing the refrigeration medium 34. It usually requires an appreciable length of time to recondition the refrigeration storing medium 34 for another unloading operation, because the compressor 16 is sized just slightly larger than is required for normal temperature maintenance in tank 11.

A pressure controller 16a is provided as illustrated in Figure 1. This pressure controller is provided so that upon increase of pressure in pipe 15 to, for example, 1 p.s.i.g., the controller actuates in response to this 1 p.s.i.g. pressure to start the compressor 16. Upon sensing a minimum pressure, for example V2 p.s.i.g. in pipe 15, the pressure controller stops compressor 16.

Propane has a normal boiling point of about -44 F., i.e., at standard atmospheric pressure. Where the propane is propane, of commercial purity, i.e., containing some ethane and butane, it is necessary to maintain the temperature in tank 11 at a temperature below 44 F., for example, --53 F., in order to maintain a maximum working pressure of 1 p.s.i.g. Such propane, i.e., commercial propane, contains some ethane and butane and has a vapor pressure of about 210 p.s.i.g. at 100 F.

A tank car such as tank car 33 is usually designed for transport of liquefied propane at atmospheric temperatures; in other words, tank 33 is a pressure vessel.

An alternate embodiment of propane flow is illustrated in Figure l in that a pipe 27a is provided for passage of liquid propane prior to pressure reduction, through a coil 28a in the refrigeration medium 34. The propane is returned to pipe 27 via pipe 27b just prior to check valve 40a. In this case valve 40a in pipe 27 is closed and the valves in pipes 27a and 27b are open. In both embodiments of flow, i.e., through pipe 27 only and through pipe 27a, coil 28a and pipe 27b, the pressure reduction step is carried out in valve 40.

In still another embodiment, coil 28a communicates through a valved, insulated pipe 36a with the lower portion of the tank 11. In this case propane added,

and particularly the vaporous propane stirs the contents of tank 11 to maintain a more nearly uniform temperature throughout its contents.

In Figure 2 is illustrated an alternate embodiment of refrigeration storage vessel and propane storage vessel as a single unit. In this figure reference numeral 51 identifies the vessel in which liquefied propane 59 is stored. A cylindrical or tubular wall 62 is provided as the side walls of the storage vessel. An outer wall 63 has a diameter somewhat larger than the diameter of the wall 62, thereby providing an annular space 64 therebetween. This annular space in this embodiment is the refrigeration medium 34 containing vessel. The refrigeration medium in this case can be the same as that described above relative to Figure 1. A spray ring is provided with spray nozzles 58, while a pipe 57 is provided for passage of propane from the outlet end of refrigeration coil 56 to the spray nozzles. A pipe 54, which is the inlet to the coil 56, corresponds to pipe 26 of Figure 1. The refrigeration medium storage space 64 in this Figure 2 is provided with an outlet pipe 61 which corresponds to outlet pipe 31 of Figure 1. Insulation 52 is also provided around the outer wall 63.

In Figure 3 is illustrated still another embodiment .of my invention in which a storage tank 65 is divided pane stored in the upper portion of tank 65, while ref- .erence numeral 34 identifies the refrigeration medium ,in the portion of the tank below the diaphragm. A coil 77 is disposed in the lower and refrigeration medium containing section, the inlet thereto being a pipe 68 and the outlet therefrom being a pipe 73. Outlet pipe 73 communicates with the spray ring containing nozzles 70. This tank also is covered with insulation 66. A pipe 67 is provided in the top of the tank for passage of vaporous propane to a compressor such as compressor 16, a pipe 69 is for outlet of liquefied gas and pipe 75 is for inlet, and outlet of refrigeration medium. Pipe 67a is for pressure relief, if necessary.

The flexible diaphragm 74 can be made of various materials as desired. This diaphragm can be made of a type of metal which is sufficiently resilient to allow expansion of an aqueous refrigeration storing medium as the material is frozen. tion of tank 65 is substantially completely filled with refrigerant liquid, this diaphragm is constructed of such materials that it is depressed as the refrigerant material 34 contracts and is elevated as the refrigerant material expands.

In Figure 4 is illustrated still another embodiment of my invention in which the refrigeration storing medium 34 is merely stored in the bottom of the liquefied propane storage tank in direct contact with the propane. A means for separation of these two materials is not provided in this case. Storage tank 81 is illustrated as containing a heat exchange coil 87 which is completely covered with refrigeration storing medium 34. On the upper surface of medium 34 is stored a quantity of liquefied propane S8. A pipe communicates with the inlet end of coil 87, while a pipe 90 leads from the outlet end of coil 87' to a ring containing spray nozzles 89. A pipe 83 serves as outlet for vaporous propane to a compressor corresponding to compressor 16 vof Figure 1. This tank of Figure 4 is also provided with a thick layer of insulation 82. Pipe 83a is for pressure relief, if necessary.

Storage tanks 11, 51, 65 and 81 are provided respectively with liquid propane outlet pipes 32, 55, 69 and 84 respectively. These pipes are for passage of storage propane to vaporization equipment or points of use. Tank 51 is provided with pipe 61, while tanks 65 and 81 are provided respectively with pipe 75 and 91 for inlet or outlet of refrigeration storing medium. A vent 62a is provided in the upper portion of the annular refrigeration storage medium containing space of Figure 2.

Pure propane at F. has a vapor pressure of about p.s.i.g., at 32 F. it has a vapor pressure of about 53 p.s.i.g., and at 0 F. it has a vapor pressure of about 24 p.s.i.g. Thus, even at the low temperature of 0 F. a very thick walled tank would be required to store liquefied propane under its own vapor pressure and particularly so when large tanks such as those capable of holding a million gallons or more of propane are used. Thus, by storing propane at from about atmospheric to about 1 p.s.i.g. considerably less steel is required for constructing such a tank. By using the refrigeration storage as herein disclosed, I am able to construct a large scale propane storage plant for considerably less capital investment than would be required if high pressure, that is, thick wall, vessels were used.

As an example of an amount of tonnage of steel saved by practicing this invention, when compared to use of standard prior art high pressure tanks, is the following.

250,000 bbl. storage Prior Art 11.1. (250 p.s.i.g.) storage One dome roof tank+12,500

bbl. ref. tank Standard 30,000 gal. tanks, 395 tanks req. Each tank=37 tons steel Total steel (395 tanks) =14,615 tons.--"

Dome-roof tank=925 tons. Brine or Ref. tank=55 tons. Total Steel=980 tons.

Furthermore, since this por-.

When using the apparatus and method of this invention, which involves continuous pressure and temperature maintenance by compression and atmospheric condensing of the compressed propane, a relatively small compression unit and condenser unit are required. In this manner capital investment is further reduced. Even with the low pressure storage tank and the low refrigeration capacity of the compression-condenser equipment, I am able to transfer appreciable volumes of liquid propane from atmospheric temperature to the herein disclosed low propane storage temperature.

I prefer, according to this invention, to store liquid propane at a temperature relatively close to its normal boiling point in case the propane is pure propane, and at a temperature slightly above the boiling point of the liquid stored in case the propane is of a commercial quality. I store pure propane at a temperature of about --40 F. At this temperature its vapor pressure is only about 1 p.s.i.g. However, for commercial quality propane I store it at about 50 to -55 F., that is, a few degrees above the boiling point of the commercial product.

If desired, in place of using atmospheric air for cooling the propane condenser, a refrigeration cycle involving ammonia, ethane or even propane as refrigerant can be used. "If propane is used, it is withdrawn from the propane in storage. Such propane used for refrigeration purposes must be dry and free from moisture, or as commonly termed, it is of refrigeration grade. Any suitable type of compressor 16 or condenser 17 can be used. 'The liquid level sensing means 23 is illustrated in Figure l as being a float, but it is obvious to those skilled in the art that other suitable type of liquid level sensing means can be used. A suitable type of thermal insulation is, of course, used. All pipes in addition to the several vessels which contain materials below atmospheric temperature are insulated.

The pressure controller assembly 16a, as mentioned, is so adjusted as to start pump 16 at about 1 p.s.i.g. and to close it ofi when the pressure in tank 11 reaches about /2 p.s.i.g. Pressure in tank 11 should not be permitted to decrease to a value below ambient atmospheric pressure so that there will be no tendency to collapse the tank.

According to this invention, and particularly in summer weather a transfer pump is usually not needed in pipe 27. However, if desired, a pump can be installed in this pipe. When unloading LP gas, such as propane, butane, or mixture of these, a transfer pump is frequently advantageous to expedite the unloading operation. With the pressure being reduced through valve 40 to 1 p.s.i.g. (pressure in tank 11) or very near to this pressure, is another reason why a transfer pump is not required in pipe 26. In this manner a tank car can be unloaded to the extent that all liquid is removed and vapor is removed until the remaining vapor has a pressure approaching the pressure maintained in the storage tank. In conventional systems a tank car is considered unloaded when the propane vapor has been reduced to 10 p.s.i.g. or to a pressure somewhat higher than 10 p.s.i.g.

Another advantage in the herein disclosed low temperature storage system is that a larger volume of liquid can be stored at -50 F., for example, then at +60 F., in tanks of equal volume. As is well known in the hydrocarbon art, hydrocarbons possess a high temperature coeificient of expansion. Thus, when 100 bbls. of a hydrocarbon product are delivered at 60 -F., then placed in storage at S F., the hydrocarbon product occupies about 15 percent less volume than it did at +60 F. By the same token 287,000 bbls. propane at a temperature of 60 'F. can be stored in a space of 250,000 bbls. volume at -'50 F.

Valves and other auxiliary equipment have not necessarily been shown for purposes of simplicity, but the need and use of such equipment will be readily understood by those skilled in the art.

While certain embodiments of the invention have been described for illustrative purposes, ,the invention obviously is-not limited thereto.

-I claim:

1. A liquefied .gas storage system comprising, in combination, a storage vessel having an outlet, at sprayin said storage vessel, a refrigeration V SS6l, a first heat exchange coil in ,said refrigeration vessel, a first conduit communicating said first coil with said spray, a second heat exchange coil, a second conduit communicating said outlet with said second heat exchange coil, a compressor in said second conduit for compressing vapor from said outlet, 2. third conduit communicating said second heat exchange coil with said first heat exchange coil, and an expansion valve in said third conduit.

2. A liquefied gas storage system comprising, in combination, a storage vessel having an outlet, a spray in said storage vessel, a refrigeration vessel, a first heat exchange coil in said refrigeration vessel, a first conduit communicating said first coil with said spray, a second heat exchange coil, a second conduit communicating said outlet with said second heat exchange coil, a compressor in said second conduit for compressing vapor from said outlet, a surge vessel, a third conduit communicating said second heat exchange coil with said surge vessel, a fourth conduit communicating said surge vessel with said first heat exchange coil for passage of liquid thereto, an expansion valve in said fourth conduit, a liquid level sensing means in communication with the interior of said surge vessel, and control means disposed so as to operate said valve in accordance to level of liquid in said surge tank as sensed by said sensing means.

3. A liquefied gas storage system comprising, in combination, a storage vessel having an outlet in its upper portion, a spray nozzle in said storage vessel, a refrigeration vessel, a first heatexchange coil in said refrigeration vessel, a first conduit communicating said heat exchange coil with said spray nozzle, a condenser, a second conduit communicating said outlet with one end portion of said condenser, a compressor in said second conduit for compressing vapor from said outlet, a fan disposed to blow air over said condenser, a surge vessel, a third conduit communicating the other end portion of said condenser with said surge vessel, a fourth conduit com.- municatingsaid surge vessel with said first heat exchange coil for passage of fluid, an expansion valve in said fourth conduit, a liquid level sensing means in communication with the interior of said surge vessel, control means dis posed so as to operate said valve in accordance to the level of liquid in said surge vessel as sensed by said sensing means, a source of liquefied gas, and a fifth conduit communicating said source of liquefied gas with said fourth conduit intermediate said valve and said first heat exchange coil.

4. The storage system of claim 3 wherein said refrigeration vessel comprises an insulated vessel disposed at a spaced distance from said storage vessel.

5. The storage system of claim 3 wherein said refrigeration vessel is disposed within said storage vessel.

6. The storage system of claim 5 wherein said storage vessel and said refrigeration vessel comprise, in combination, an upright first tubular member having upper and lower end closures, said outlet being disposed in the upper end closure, a second tubular member disposed within said first tubular member, said first tubular member and said second tubular member being disposed along a common vertical axis, the bottom end of said second tubular member being fixed fluid tight to said lower end closure, said second tubular member having a smaller diameter than the diameter of said first tubular vessel so as to provide an annulus therebetween, said refrigeration vessel being defined by said first tubular vessel, said second tubular member and the portions of the upper and lower ,end closurestherebetween, and said storage vessel being defined by said second tubular member and the remaining portions of said upper and lower end closures.

7. The storage system of claim wherein said storage vessel and said refrigeration vessel comprise, in combination, an upright tubular member having upper and lower end closures, said outlet being disposed in the upper end closure, a fluid tight flexible diaphragm disposed across said tubular member intermediate its ends, said storage vessel being defined as the space in said tubular member intermediate the upper end closure and said diaphragm and said refrigeration vessel being the space in said tubular member intermediate said diaphragm and the lower end closure.

8. The system of claim 5 wherein said storage vessel and said refrigeration vessel comprise a tubular member having its axis vertically disposed and upper and lower end closures, said outlet being disposed in the upper end closure, said first heat exchange coil being disposed in the lower portion of said tubular member, said refrigeration vessel being defined as the space in said tubular member intermediate the lower end closure and the top level of said first heat exchange coil and said storage vessel being defined as the space in said tubular member intermediate the upper end closure and the top level of said first heat exchange coil.

9. A method for maintaining a liquefied gas in a storage zone in a chilled condition and at a pressure near atmospheric pressure comprising Withdrawing vapor of said liquefied gas from said storage zone, compressing the withdrawn vapor, condensing the compressed vapor thereby producing condensate, reducing the pressure of said condensate to a pressure intermediate that of the condensate and said pressure near atmospheric pressure in an expansion step thereby producing refrigerated condensate and vapor, passing said refrigerated condensate and vapor in indirect heat exchange with a refrigeration storage medium wherein the latter is chilled and a portion of the refrigerated condensate is vaporized, and spraying the remaining condensate and vapor into said storage zone at said pressure near atmospheric pressure to produce chilled liquid in storage and vapor.

10. A method for maintaining liquefied gas in a storage zone in a chilled condition at a pressure near atmospheric pressure during periods of addition of liquefied gas from an extraneous source, said liquefied gas from said extraneous source having a higher temperature than the liquefied gas in said storage zone, comprising,

withdrawing vapor of said liquefied gas from said storage zone, compressing the withdrawn vapor, condensing the compressed vapor by indirect heat exchange with the atmosphere thereby producing condensate, reducing the pressure of said condensate to a pressure intermediate that of the condensate and said pressure near atmospheric pressure in an expansion step thereby producing refrigerated condensate and vapor, adding to this refrigerated condensate and vapor said liquefied gas from said extraneous source, passing the combined refrigerated liquefied condensate, vapor and added liquefied gas in an indirect heat exchange step with a previously chilled refrigerated storage medium wherein the effluent emerges from said heat exchange step at substantially the temperature of said refrigeration storage medium and subsequently spraying said effluent into said storage zone at said pressure near atmospheric pressure thereby producing 0ondensate in said chilled condition.

11. A method for maintaining liquefied gas in a storage zone in a chilled condition at a pressure near atmospheric pressure during periods of addition of liquefied gas from an extraneous source, said liquefied gas from said extraneous source having a higher temperature than the liquefied gas in said storage zone, comprising, withdrawing vapor of said liquefied gas from said storage zone, compressing the withdrawn vapor, condensing the compressed vapor thereby producing condensate, reducing the pressure of said condensate to a pressure intermediate that of the condensate and said pressure near atmospheric pressure thereby producing refrigerated condensate and vapor, adding to this refrigerated condensate and vapor said liquefied gas from said extraneous source, passing the combined refrigerated condensate, vapor and added liquefied gas in an indirect heat exchange step with a previously chilled refrigerated storage medium from which efiluent emerges at substantially the temperature of said refrigeration storage medium and subsequently spraying said effluent into said storage zone at said pressure near atmospheric pressure thereby pro-- ducing condensate in said chilled condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,448,403 Turner Aug. 31, 1948 2,550,886 Thompson May 1, 1951 2,895,305 Reed July 21, 1959 

